Look at the output drive specs of the CD40106 vs the input drive current requirement of the ULN2003.http://www.ti.com/lit/ds/symlink/cd40106b.pdfhttp://www.ti.com/lit/ds/symlink/uln2003a.pdfThe CD40106 is really marginal to drive the ULN2003.Find a better part.
±4-mA Output Drive at 5 V
Thank you, I'm going to buy a SN74HC04 the next week, It should had the right parameters for the ULN2003. Hoping to solve the problem.DatasheetQuote±4-mA Output Drive at 5 V
Try putting a 10K pullup to 12V on the ULN2803 outputs to help bring the cathodes high.